Early detection of low blood oxygen is important in a wide variety of medical applications, and oximetry was developed to study and to measure, among other things, the oxygen status of blood. One type of oximetry, pulse oximetry, employs a sensor attached to a patient in order to output a signal indicative of a physiological parameter of the patient, such as, for example, the patient's blood oxygen saturation.
A pulse oximeter sensor generally uses a number of sensor components, such as one or more energy emission devices like red and infrared LED emitters, and an energy detection device like a photodiode detector. The sensor is generally attached to a measurement site such as a patient's finger, toe, ear, forehead, foot, hand, heel or the like, using an attachment mechanism such as a disposable tape, reusable housing, Velcro strap, or the like. The attachment mechanism positions the emitter and detector in proximity to the measurement site, such that the emitter projects energy into the blood vessels and capillaries of the measurement site, and the photodiode detector then detects the attenuated energy. The emitted energy can be light or other forms of energy. The detector communicates a signal indicative of the detected attenuated energy to a signal processing device such as an oximeter. The oximeter generally calculates, among other things, one or more physiological parameters of the measurement site.
In sensors where the detector detects emissions through the measurement site, it is generally desirable to position the detector opposite the emitter around the measurement site, such as, for example, above and below a finger. However, sensors are produced in a limited number of sizes and shape configurations, while patients have, for example, fingers and toes of many different sizes and shapes.
In addition, the attachment mechanism and the electronic components of a sensor are generally curved around a measurement site in a manner detrimental to one or more elements of the sensor. For example, the attachment mechanism generally wraps around the measurement site at an approximate “inner circle” having a first radius, while the electronic components such as the flexible circuits are generally fixedly attached to the attachment mechanism. Accordingly, the electronic components can form an approximate “outer circle” having a second radius unequal to the first radius. However, because the attachment mechanism generally does not move independently with respect to the electrical components, attachment of the sensor to the measurement site can exert forces on the electrical components, such as, for example, exerting forces which try to lengthen, or longitudinally stretch the electrical components to account for an increased radius thereof. The forced stretching can damage the electrical components of a flexible circuit, such as the conductive traces.